Multiple Sclerosis (MS) is a neurological disease affecting more than 1 million people worldwide. It is the most common cause of neurological disability in young and middle-aged adults and has a major physical, psychological, social and financial impact on subjects and their families, friends and bodies responsible for health care (EMEA Guideline, 2006).
It is generally assumed that MS is mediated by some kind of autoimmune process possibly triggered by infection and superimposed upon a genetic predisposition. It is a chronic inflammatory condition that damages the myelin of the Central Nervous System (CNS). The pathogenesis of MS is characterized by the infiltration of autoreactive T-cells from the circulation directed against myelin antigens into the CNS (Bjartmar, 2002). In addition to the inflammatory phase in MS, axonal loss occurs early in the course of the disease and can be extensive over time, leading to the subsequent development of progressive, permanent, neurologic impairment and, frequently, severe disability (Neuhaus, 2003). Symptoms associated with the disease include fatigue, spasticity, ataxia, weakness, bladder and bowel disturbances, sexual dysfunction, pain, tremor, paroxysmal manifestations, visual impairment, psychological problems and cognitive dysfunction (EMEA Guideline, 2006).
MS disease activity can be monitored by cranial scans, including magnetic resonance imaging (MRI) of the brain, accumulation of disability, as well as rate and severity of relapses. The diagnosis of clinically definite MS as determined by the Poser criteria (Poser, 1983) requires at least two neurological events suggesting demyelination in the CNS separated in time and in location. A clinically isolated syndrome (CIS) is a single monosymptomatic attack suggestive of MS, such as optic neuritis, brain stem symptoms, and partial myelitis. Patients with CIS that experience a second clinical attack are generally considered to have clinically definite multiple sclerosis (CDMS). Over 80 percent of patients with a CIS and MRI lesion go on to develop MS, while approximately 20 percent have a self-limited process (Brex, 2002; Frohman, 2003). Various MS disease stages and/or types are described in Multiple Sclerosis Therapeutics (Duntiz, 1999). Among them, relapsing-remitting multiple sclerosis (RRMS) is the most common form at the time of initial diagnosis. Many subjects with RRMS have an initial relapsing-remitting course for 5-15 years, which then advances into the secondary progressive MS (SPMS) disease course. Relapses result from inflammation and demyelination, whereas restoration of nerve conduction and remission is accompanied by resolution of inflammation, redistribution of sodium channels on demyelinated axons and remyelination (Neuhaus, 2003; Noseworthy, 2000).
In April 2001, an international panel in association with the National MS Society of America recommended diagnostic criteria for multiple sclerosis. These criteria became known as the McDonald Criteria: The McDonald Criteria make use of MRI techniques and are intended to replace the Poser Criteria and the older Schumacher Criteria (McDonald, 2001). The McDonald Criteria was revised in March 2005 by an international panel (Polman, 2005) and updated again in 2010 (Polman, 2011).
Intervention with disease-modifying therapy at relapsing stages of MS is suggested to reduce and/or prevent accumulating neurodegeneration (Hohlfeld, 2000; De Stefano, 1999). There are currently a number of disease-modifying medications approved for use in relapsing MS (RMS), which includes RRMS and SPMS (The Disease Modifying Drug Brochure, 2006). These include interferon beta 1-a (Avonex® and Rebif®), interferon beta 1-b (Betaseron®), glatiramer acetate (Copaxone®), mitoxantrone (Novantrone®), natalizumab (Tysabri®) and Fingolimod (Gilenya®). Most of them are believed to act as immunomodulators. Mitoxantrone and natalizumab are believed to act as immunesuppressants. However, the mechanisms of action of each have been only partly elucidated. Immunosuppressants or cytotoxic agents are used in some subjects after failure of conventional therapies. However, the relationship between changes of the immune response induced by these agents and the clinical efficacy in MS is far from settled (EMEA Guideline, 2006).
Other therapeutic approaches include symptomatic treatment which refers to all therapies applied to improve the symptoms caused by the disease (EMEA Guideline, 2006) and treatment of acute relapses with corticosteroids. While steroids do not affect the course of MS over time, they can reduce the duration and severity of attacks in some subjects.
Fingolimod
Fingolimod (Fingolimod, Gilenya™) is a new class of drugs called sphingosine 1-phosphate (S1P) receptor modulators. These medicines reduce inflammation and may also have a direct beneficial effect on cells in the central nervous system (CNS). Upon administration, fingolimod is phosphorylated by sphingosine kinase to form the active metabolite fingolimod-phosphate-Fingolimod is therefore a prodrug. Fingolimod-phosphate binds the sphingosine 1-phosphate receptors S1PR-1, S1PR3, S1PR4 and S1PR5 with high affinity and thereby blocks the capacity of leukocytes to migrate from lymph nodes into the peripheral blood. These receptors are also known as EDG receptors, and are all members of the rhodospin-like GPCR family, the largest single historical successful family of drug targets (GPCR SARfari: S1PR-1 (aka. EDG1)). The curative mechanism underlying fingolimod's therapeutic effect is unknown but may involve a reduced migration of lymphocytes into the CNS. The chemical structure of fingolimod was derived from the myriocin (ISP-1) metabolite of the fungus Isaria sinclairii. It is a structural analogue of sphingosine and gets phosphorylated by sphingosine kinases in the cell (most importantly sphingosine kinase 2) (Paugh S W 2003; Billich A, 2003; Sanchez, T, 2003). The molecular biology of phospho-fingolimod is thought to lie in its activity at one of the five sphingosine-1-phosphate receptors, S1PR1(H1a T, 2001). It can sequester lymphocytes in lymph nodes, preventing them from moving to the central nervous system for auto-immune responses in multiple sclerosis and was originally proposed as a anti-rejection medication indicated post-transplantation. It has been reported to stimulate the repair process of glial cells and precursor cells after injury (Alejandro Horga, 2008). Fingolimod has also been reported to be a cannabinoid receptor antagonist (Paugh S W, 2006), a cPLA2 inhibitor (Payne S G, 2007) and a ceramide synthase inhibitor (Berdyshev E V, 2009).
